Constant Force Tourbillon Ref. 1FCAR.B01A.C112C

Arnold & Son pushes precision chronometry ever further with
the Constant Force Tourbillon, featuring a patented constant force
device with 60-second tourbillon and true beat seconds. The
symmetrical movement architecture of the Constant Force Tourbillon
movement pays tribute to Arnold & Sons' historic marine
chronometers. At the top, two visible mainspring barrels and the
constant force device provide optimal power to the tourbillon at
the bottom of the dial.

The Constant Force Tourbillon is part of the Royal Collection
and, like every other model from Arnold & Son, features an
in-house mechanical movement. John Arnold (1736-1793) was
constantly searching for higher precision in his timepieces, as the
more accurate the chronometer, the more precise the calculation of
longitudinal (east/west) position at sea. Arnold and his son were
the first to develop and produce technically superlative (but
reasonably priced) marine chronometers in significant
quantities.

Constant force is an essential element in the quest for higher
precision because it is difficult regulating a consistent output,
e.g. isochronal time when the power input from the mainspring is
constantly changing. Imagine trying to drive a car at a consistent
speed with an engine that continually varies its power output.

To maximize power consistency in the Constant Force Tourbillon,
Arnold & Son began at the beginning, i.e. the mainspring
barrel, as this is the source of the movement's power. Instead of
using just one mainspring barrel, which would produce significantly
different amounts of torque between fully wound and nearly empty,
the Constant Force Tourbillon has two symmetrical barrels in
series, visible dial side at 10:30 and 1:30. The first mainspring
barrel alone powers the gear train, while the second barrel tops up
the first whenever its torque output drops below optimal. This
ensures that the power to the regulator flows as constantly as
possible.

The Constant Force Tourbillon features a patented constant force
mechanism. Instead of power from the mainspring feeding directly to
the escapement/tourbillon, it charges a small hairspring which in
turn releases a consistent amount of power to the
escapement/tourbillon once each second. The device also drives the
true-beat seconds hand (also known as jumping seconds or dead
seconds), a highly cherished Arnold & Son complication. When
the power from the mainspring drops below that required by the
constant force mechanism, the movement stops rather than running at
lower precision. The constant force device rotates once per minute
in increments of one second, visually mirroring the rotation of the
constantly rotating tourbillon cage. The bridges supporting the
constant force regulator and tourbillon are also symmetrical, both
horizontally with each other and vertically with the barrel
bridges.

While the constant force mechanisms optimize precision with the
movement in stable positions, the 60-second tourbillon averages out
gravitational errors on the escapement by constantly rotating it
through 360°. The difference between the rotating tourbillon and
rotating constant force device is that the former turns continually
while the latter steps in increments of one second.

The Constant Force Tourbillon is a limited edition of 28
timepieces, and is available in a 46 mm 18-carat red gold case with
anti-reflective sapphire crystal and sapphire display back for
viewing the superbly hand-finished movement.